1. Technical Field
The present invention relates generally to an easy-to-install structure of a distance sensor which may be used with an obstacle detection system for vehicles.
2. Background Art
Ultrasonic sensors are known which are used as automotive distance sensors (also called range sensors) which measure the distance between the vehicle and an obstacle using an ultrasonic wave. Some of modern vehicles such as automobiles are equipped with an obstacle detector called a clearance sonar system for assisting the driver in parking the vehicle. The clearance sonar system has a plurality of ultrasonic sensors (e.g., two installed in a front bumper, and four installed in a rear bumper) and works to measure the amount of time required by the ultrasonic wave, as transmitted from each of the ultrasonic sensors, to travel to and return from an obstacle and determine the distance between the vehicle and the obstacle based on the measured amount of time. When such a distance decreases below a given value, the clearance sonar system alerts the driver by sound. For instance, Japanese Translation of PCT Application Publication No. 2000-513296 (corresponding to U.S. Pat. No. 6,227,501 B1) teaches the ultrasonic sensor.
FIG. 12 illustrates a conventional ultrasonic sensor 3′. The installation of the ultrasonic sensor 3′ in a mount hole 47 of a bumper 2 is achieved by disassembling the ultrasonic sensor 3′ into a bezel 49′ and a casing 45′, placing the bezel 49′ and the casing 45′ outside and inside the bumper 2, respectively, and joining them together through the mount hole 47.
The ultrasonic sensor 3′ has a plurality of metal springs 53′ installed in the bezel 49′ in which a sensor device 41′ is retained. The metal springs 53′ engage a peripheral edge of the mount hole 47 of the bumper 2 to secure the ultrasonic sensor 3′ to the bumper 2. The metal springs 53′ are made by, for example, a multi-forming machine and then assembled in the bezel 49. Specifically, the installation of the ultrasonic sensor 3′ to the bumper 2 requires an additional step of installing the metal springs 53′ in the bezel 49′, which results in an increase in overall production cost of the ultrasonic sensor 3′.
The joining of the bezel 49′ and the casing 45′ requires two steps of inserting the bezel 49′ into the mount hole 47 of the bumper 2 and then fitting the casing 45′ in the bezel 49′. This results in an increase in time consumed to fix the ultrasonic sensor 3′ to the bumper 2. If the assembly of the bezel 49′ and the casing 45′ is inserted into the mount hole 47 of the bumper 2, it may result in plastic deformation of the metal springs 53′ when passing through the mount hole 47, which leads to a failure in nipping the wall of the bumper 2 between the bezel 49′ and the casing 45′. It is also difficult to use the ultrasonic sensor 3′ with bumpers having different thicknesses.